Most alkali metals have a silvery white appearance with the exception of caesium which is golden yellow.
They are all soft metals and typically can be cut with a knife. The softness of the metal increases within the
group; caesium is the softest of the alkali metals.
Alkali metals are generally very reactive and oxidise in the air. The reactivity increases within the group,
with lithium having the lowest reactivity and caesium the highest. Therefore, all alkali metals except lithium
have to be stored in mineral oil. Lithium as an exception is normally stored under inert gas such as argon.
Nevertheless, lithium, sodium and potassium can be handled in air for a short time, whereas rubidium and
caesium have to be handled in an inert gas atmosphere.
All alkali metals react violently with water with the formation of the metal hydroxide and hydrogen. Again,
lithium is the least reactive alkali metal and reacts ‘only’ quickly with water, whereas potassium, rubidium
and caesium are more reactive and react violently with water.
Reference Inorganic chemistry by Huhee
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